In a wireless communication, there is a problem that interference occurs with other systems or other appliances. Especially, in 2.4 GHz band, which is used in a wireless LAN or Bluetooth (trademark) etc., a problem is easily possible to occur that the band is simultaneously employed among a plurality of systems or among a plurality of access points in the same system. Accordingly, measure to avoid interference among the systems or the access points is required.
Generally, as a method to avoid the interference, a channel hopping scheme is employed which changes a channel according to a hopping pattern of predetermined channels to perform communication. In the IEEE802. 15. 4, a method is standardized in which a node searches a new channel by iteratively the following processes: specifying a candidate channel from channels included in a hopping pattern, and performing channel change to the candidate channel and channel scan. In the method, however, it is required to scan some channels even if a number of candidate channels to be scanned is restricted. Therefore, it takes time to perform the channel change and the channel scan while power consumption increases.
On the other hand, in a communication system in which a child appliance functions as a relay node, the following method is proposed. Specifically, a parent appliance which uses a channel #f1 notifies channel numbers (i.e., channel Nos.) of the previous channel #f0 and a change candidate channel #f2 to the child appliance. The child appliance which is notified of the channel numbers uses the previous channel #f0 to notify the channel numbers of the current communication channel #f1 and the change candidate channel #f2 to other child appliance(s) which directly does not communicate with the parent appliance. In the method, the time taken for the channel change is shortened although the other child appliance only follows up one channel before the channel change. Therefore, in a case where there is a child appliance which is sleeping for a long time, the child appliance is likely to not be able to follow up a latest channel.